1. Field of the Invention
The present invention relates to an exposure-scanning device, and more particularly to an exposure-scanning device of a mirror scanning type which is installed into an image forming apparatus such as an electrophotographic copying machine, facsimile or the like for performing a slit exposure by moving mirrors for exposure-scanning.
2. Prior Art
A conventional exposure-scanning device of a mirror scanning type installed into an electrophotographic copying machine or the like comprises a pair of guide members horizontally arranged parallel to each other, scanning members slidably provided to the pair of guide members and having an exposure-scanning mirror or the other elements mounted thereon and a pair of upper and lower rollers provided at both ends of each scanning member for enabling the scanning member to slidably move. Each of the guide members is sandwiched between these upper and lower rollers.
The exposure-scanning device of the above-mentioned type is assembled as follows. First, the upper roller is mounted on the scanning member through the bracket to which the upper roller is attached. Thereafter, the resultant scanning member is placed on the guide members to be supported by the upper roller. Subsequently, the bracket having provided with the lower roller is mounted to the scanning member on the guide members. The bracket with the lower roller is screwed to or bolted with a nut to the scanning member.
However, the above-mentioned assembling operation of the exposure-scanning device entails a following problem. Specifically, such an assembling operation requires a screwing operation for fixing the bracket having the lower roller to the scanning member with a screw or a bolt and nut. The screwing operation causes the bracket having the lower roller to move in the screwing direction in accordance with the rotation of the screw or bolt in the screwing direction (i.e., normally in the clockwise direction).
The unintentional movement of the bracket changes the space between the upper and lower rollers which is set before the screwing operation, whereby disadvantages occur such that the lower roller does not get in contact with the guide member or the lower roller is in pressing contact with the guide members with a pressure different from the predetermined pressure. When the scanning member slidably moves on the guide member with such disadvantages, the mirror or the other elements mounted on the scanning member cannot perform a stable scanning operation. Therefore, an image blur may occur upon image formation.